Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C27/00—Rotorcraft; Rotors peculiar thereto
  • B64C27/32—Rotors
  • B64C27/37—Rotors having articulated joints
  • B64C27/39—Rotors having articulated joints with individually articulated blades, i.e. with flapping or drag hinges
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C27/00—Rotorcraft; Rotors peculiar thereto
  • B64C27/32—Rotors
  • B64C27/35—Rotors having elastomeric joints
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C27/00—Rotorcraft; Rotors peculiar thereto
  • B64C27/32—Rotors
  • B64C27/46—Blades
  • B64C27/473—Constructional features
  • B64C27/48—Root attachment to rotor head
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C27/00—Rotorcraft; Rotors peculiar thereto
  • B64C27/51—Damping of blade movements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C27/00—Rotorcraft; Rotors peculiar thereto
  • B64C27/32—Rotors
  • B64C27/46—Blades
  • B64C27/473—Constructional features
  • B64C27/50—Blades foldable to facilitate stowage of aircraft

Definitions

• Helicopter rotor blades are subject to aerodynamic and inertial forces that, in turn, create vibratory (oscillatory) motions because of the non-uniform flow environment in which these aircraft are designed to operate.
• the aerodynamic forces can cause the rotor to cone and flap as it rotates.
• the rotor cones all blades move up or down in unison.
• the rotor flaps opposing blades move in opposite directions. This coning and flapping are accommodated by the rotor hub either by bearings or by deflection of structural members.
• This bearing or flexure is important because it determines the rotor hub moment used to control the helicopter and, therefore, this location is usually a design parameter that must be controlled.
• the component described as a“Yoke” in the present technology is designed with a flexure that provides this deflection to permit the blade to cone and to flap.
• the term“virtual hinge” is used.
• the location of this virtual hinge is specified by the intersection of two lines drawn tangent to the inboard and outboard slope of the deflected yoke.
• the flap moment at the hub is the same as if there was a pure hinge.
• the yoke of some embodiments of the present technology is tapered to give the precise moment desired at the hub for a specified amount of blade flapping.
• the present disclosure provides an advanced technology hub for rotor aircraft.
• Figure 1 depicts a schematic, elevation view of a prior art helicopter and demonstrates coning and flapping of the rotor commonly caused by aerodynamic and inertia forces on the helicopter rotor.
• Figure 2 depicts a partial, isometric view of one embodiment of a rotor mast and hub of a soft in-plane rotor of the present technology. Manual blade fold for transportation or storage is illustrated.
• the cross-section A-A is presented in Figure 5.
• Figure 3 depicts a partial, exploded view of one embodiment of a rotor hub of the present technology illustrating the assembly of major comments.
• Figure 4 depicts the assembly of the joint accommodating blade pitch change and the transfer of shears between the grip and the yoke.
• Figure 5 presents the details of Section A-A referenced in Figure 2.
• Figure 6 describes the assembly of the blade to the outboard end of the grip.
• the yoke may be made of graphite epoxy, which allows embodiments of the rotor hub design to have a tapered thickness and stiffness to achieve a precise location of the virtual flapping hinge.
• a lag hinge may be incorporated at an outboard end of the grip (inboard end of the blade) that accommodates small lag motion and reduces moments due to blade inertial and aerodynamic forces.
• a lag spring/damper may be incorporated that is placed along the blade radial axis providing a compact installation that also reduces drag. This arrangement also allows blade folding by disengaging the damper attachment pin and rotating the blade around the lag hinge. This reduces the space required to hanger or store the aircraft.
• a hub plate 12 attaches a yoke 14 to a mast 16 and is at least partially responsible for transmitting torque.
• a yoke arm 18 accommodates flapping and coning and reacts blade beam and chord shears. The yoke arm 18 does not, however, react CF.
• Grip 16 transmits CF from a blade 20 to a hub center section 22 and beam 24 and chord shears 26 to the yoke 14. This accommodates blade attachment and blade lead- lag and damper motion, providing a soft in-plane rotor.
• Pitch hinges 28 provide blade pitch change for the blade 20 with-out transmitting CF load.
• a tension-torsion strap 30 provides tension CF load path structure without reacting torsion or bending.
• a bearing/bushing 32 permits blade lag motion.
• An elastomeric spring damper 34 creates moments about the lag hinge 36 to optimize the natural frequency of the rotor lag mode and provides damping to help stabilize this mode.
• a four-bladed rotor hub assembly 10 is mounted rigidly on the upper end of a mast 16 by means of a pair of hub clamp plates 36 and 38.
• an integral flange on the mast may also be used instead of the lower hub plate.
• the hub assembly 10 is characterized by a flat carbon-epoxy yoke center section 22, which is secured between the lower face of the upper clamp plate 36 and the upper face of the lower clamp plate 38.
• the upper hub clamp plate 36 includes a plate with an integral splined sleeve 42 that extends thru the hub assembly 10.
• the lower hub plate 38 is a simple flat ring that attaches to the upper plate 36 to complete the hub assembly 10.
• the hub 10 may be molded with the arms coned relative to the hub center section to reduce the steady stresses. If employed, this feature is described as “pre-cone”.
• FIG. 3 depicts an exploded view of the carbon-epoxy yoke arm 44.
• Each yoke arm has two hinge fittings 46 fastened to the trailing edge.
• Each fitting has two vertical tabs 48.
• a tension-torsion strap 30 attaches to a steel fitting 50 to transfer centrifugal forces to the hub plates 12 and into the mast 16.
• the steel fitting 50 attaches to the hub plates 12 in a manner that prevents the centrifugal forces from being reacted by the carbon epoxy yoke center section.
• the strap 30 is soft torsionally to accommodate pitch change motion from the rotor controls.
• a blade grip 52 attaches to the outboard end of the tension-torsion strap 30 with a bolt 54.
• a pitch hom 56 attaches to the inboard end of the grip 52, or alternately, is an integral part of the grip 52. Integral internal webs 58, shown in Figure 4, are included in each end of the grip 52. In another embodiment of this design, the tension-torsion strap 30 may be eliminated by extending the length of the grip 52 and attaching the root end of the grip 52 to a bearing attached to link 50.
• Embodiments of the grip 52 attach to the yoke 14 as depicted in View A of Figure 3, which is shown in greater detail in Figure 4.
• a stainless-steel race and lined spherical bearings 60 are press fit inside the inboard and outboard internal webs 58 of the grip 52.
• the inside of the race 60 is lined for easy movement of the mono-ball inside the race to prevent the assembly from reacting a moment in any direction.
• the mono-ball spherical is lined on the inside IML to provide a low friction surface for the bearing to slide on the sleeved shoulder bushing 62.
• This assembly provides for rotation of the bearing to accommodate blade pitch change while providing a load path for blade vertical and inplane shears to be transmitted to the grip52.
• the grip 52 is then attached to the vertical arms 48 of the hinge fittings 46 with a sleeved shoulder bushing 62.
• the length of the shoulder bushing 62 is carefully controlled so that the vertical arms on the hinge fittings 46 are not subjected to bending stresses and to accommodate small axial motions to prevent centrifugal forces from being transmitted to the yoke 14.
• the Section A-A view of Figure 5 also illustrates these details.
• the hinge fittings are attached to the yoke to complete the hub assembly.
• the outboard end of the grip 52 shown in Figure 6, has two in-line holes 64 and provisions for securing the blade 20, attaching a lag spring and damper, and accommodating blade fold.
• the larger hole on the inboard side of the grip accommodates an elastomeric bushing 66.
• the blade 20 has a mating hole on the root end and a bolt 68 attaches the blade 20 to the grip 52.
• the grip bearing is the primary load path for transferring centrifugal forces from the blade 20 to the grip 52.
• the bearing also acts as a lag hinge, providing flexibility for the blade lead and lag motion and tuning the first blade mode natural frequency below l/rev which is characteristic of the descriptor“soft-in-plane”.
• the smaller hole on the outboard end of the grip 52 is oversized to permit the blade lead-lag motion and to act as a stop when contacted by the bolt 70 which attaches the damper 72 to the blade 20 and passes thru the grip 52.
• the damper 72 also contains an elastomer that provides both a damping and spring force around the lag bushing. The damping force contributes to the damping required to lag mode.
• the outboard bolt 70 is also designed as an alternate load path for centrifugal force in the event the inboard bolt fails. Manual blade fold, illustrated in Figure 2, is accommodated by disconnecting bolt 70 and rotating the blade 20 about the inboard bushing.
• a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all subranges or individual values that are between and/or inclusive of the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Aviation & Aerospace Engineering (AREA)
• Vibration Dampers (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2019
  • 2019-05-08 EP EP19800621.5A patent/EP3755623A1/de not_active Withdrawn
  • 2019-05-08 WO PCT/US2019/031284 patent/WO2019217532A1/en active Search and Examination
  • 2019-05-08 US US16/406,508 patent/US11040771B2/en active Active

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